It is well known that infections occur in about 1% to about 5% of all primary arthroplasties, and that “the economic impact, the morbidity, and the emotional trauma of prosthetic joint infection is immense and devastating to the patient and society”. Trampuz et al., Clin. Orthop., (414), 2003 pp. 69–88. The costs associated with revision surgeries and prolonged hospital stays due to deep wound infection are significant.
Postoperative wound infection (deep and superficial) in spinal implant cases for scoliosis and cerebral palsy patients has a particularly high frequency. The majority of deep wound infections in spinal cases are treated by irrigation and debridement while leaving the wound open, allowing it to heal. However, removal of the hardware associated with deep wound infections in these cases is often necessary.
It is believed that a majority of these infections occur via transmission from microbes upon the surgical gloves, the patient's skin, implants or instruments. Unlike routine systemic infections, infections associated with implants (“periprosthetic infections”) are particularly troublesome.
First, it has been reported that certain biomaterials cause an abnormal and inferior immune response. In short, a portion of the immune response is provided by the release of superoxide ions, such as hydroxyl radicals, that are lethal to microbes. However, when a periprosthetic infection occurs, it has been reported that biomaterials such as cobalt chrome alloys cause abnormal neutrophil activity, resulting in an inferior non-productive immune response. Shanbhag, J. Biomed. Mar. Res., Vol. 26, 185–95, 1992.
Second, it appears that the presence of the implant surface helps the microbes survive both the immune response and antibiotic treatment. In particular, microbes of concern attach to the implant surface and form a polymer-like glaze (or “biofilm”) between themselves and the local environment. This biofilm acts as an effective barrier to both neutrophils and antibiotics.
Although the periprosthetic infection itself is a primary concern for the patient, it is also known that the immune response triggered by the body to fight the infection also results in bone loss. In particular, the increased phagocyte concentration also increases the local concentration of tumor necrosis factor (TNF-α). The TNF-α concentration in turn upregulates the local level of osteoclasts. These increased osteoclast concentration uncouples the normal balance in bone metabolism, thereby leading to localized bone loss. This localized bone loss may result in the loosening of the implant, thereby necessitating its removal.
Prior art attempts at infection control have considered precoating spinal rods an intramedullary rods with an anti-infective coating. However, when the coatings at interconnection locations wear away, the space produced thereby leads to loose connections between the rod and the component to which it is connected.
In addition, prior art anti-infective coatings are typically cytotoxic to the microbes. This type of approach leads to building up resistance in the surviving microbes.
U.S. Pat. No. 6,503,507 (“Allen”) discloses the use of a light-activated composition that produces singlet oxygen. Allen discloses that the singlet oxygen produced therefrom is effective in killing bacteria.
U.S. Pat. No. 6,527,759 (“Tachibana”) discloses the use of light activated drugs that produce singlet oxygen.
Implant Sciences Corp. has promoted a surface treatment for percutaneous medical devices that prevents the growth of bacteria be employed the germ-fighting properties of silver coatings. U.S. Pat. No. 6,592,888 (“Jensen”) discloses the use of metallic compounds in wound dressings to produce anti-microbial effects. U.S. Pat. No. 6,605,751 (“Gibbins”) discloses the use of silver containing anti-microbial hydrophilic compositions. U.S. Patent Application 2003/0204229A1 (“Stokes”) discloses the use of a polymeric casing containing cations as biologically active agents to be used on medical implants and devices.
Ohko, J. Biomed. Mat. Res. (Appl Biomat) 58: 97–101, 2001 reports coating titania upon silicone catheters and medical tubes, and illuminating those tubes with UV light. Ohko further reported the bactericidal effect of the subsequent photocatalysis on E. coli cells. However, Ohko states that TiO2 is toxic under illumination, and that because the part of the TiO2 coating buried in the patient's body can not be illuminated, the coating should not be harmful to the body. Therefore, it appears that Ohko discourages the in vivo irradiation of titania.
U.S. Published Patent Application 2003/0125679 (“Kubota”) discloses a medical tube comprising an elastomer and a photocatalyst layer, wherein the tube is purported to have excellent antibacterial activity.
Hydrocephalus is a condition afflicting patients who are unable to regulate cerebrospinal fluid flow through their body's own natural pathways. Produced by the ventricular system, cerebrospinal fluid (CSF) is normally absorbed by the body's venous system. In a patient suffering from hydrocephalus, the cerebrospinal fluid is not absorbed in this manner, but instead accumulates in the ventricles of the patient's brain. If left untreated, the increasing volume of fluid elevates the patient's intracranial pressure and can lead to serious medical conditions such as subdural hematoma, compression of the brain tissue, dementia, impaired gait, and impaired blood flow.
The treatment of hydrocephalus has conventionally involved draining the excess fluid away from the ventricles and rerouting the cerebrospinal fluid to another area of the patient's body, such as the abdomen or vascular system. A drainage system, commonly referred to as a shunt, is often used to carry out the transfer of fluid. In order to install the shunt, typically a scalp incision is made and a small hole is drilled in the skull. A proximal, or ventricular, catheter is installed in the ventricular cavity of the patient's brain, while a distal, or drainage, catheter is installed in that portion of the patient's body where the excess fluid is to be reintroduced. To regulate the flow of cerebrospinal fluid and maintain the proper pressure in the ventricles, a pump or one-way control valve can be placed between the proximal and distal catheters. Such valves can comprise a ball-in-cone mechanism as illustrated and described in U.S. Pat. Nos. 3,886,948, 4,332,255, 4,387,715, 4,551,128, 4,595,390, 4,615,691, 4,772,257, and 5,928,182, all of which are hereby incorporated by reference. When properly functioning, these shunt systems provide an effective manner of regulating CSF in hydrocephalus patients.
After implantation and use over extended periods of time, these shunt systems tend to malfunction due to shunt occlusion. Frequently, the blockage occurs within the ventricular catheter. The obstruction can result from a number of problems, such as clotting, bloody CSF, excess protein content in the CSF, inflammatory or ependymal cells, brain debris, infection, or by choroid plexus or brain parenchyma in-growth through the openings of the ventricular catheter. Another potential cause of ventricular catheter occlusion is a condition known as slit ventricle syndrome in which the ventricular cavity collapses, thus blocking the openings of the ventricular catheter. If left untreated, the occlusion of the ventricular catheter can slow down and even prevent the ability of the shunt valve to refill, thereby rendering the shunt system ineffective.
In the past, the remedy for a clogged proximal catheter was to surgically remove and replace the catheter, which involved a risk of damage to the brain tissue or hemorrhage. The current trend is to rehabilitate the catheter in place through less invasive means. This can be accomplished in a procedure generally known as shunt or ventricular catheter revision which involves reaming the clogged catheter in its implanted state until the blockage is removed to thereby reestablish CSF flow through the ventricular catheter. Many shunt valves, such as the ones described in U.S. Pat. Nos. 4,816,016 and 5,176,627, are provided with a domed silicone reservoir that enables access to the attached ventricular catheter so that the system can be flushed out for this very reason. The self-sealing silicone dome can be pierced with a small needle to gain entry to the attached catheter, without affecting the ability of the dome to re-seal after the needle has been withdrawn. In some domed valves with right angle access, i.e., where the ventricular catheter extends at a 90 degree angle to the drainage catheter, a surgeon can gain entry to the clogged ventricular catheter percutaneously by inserting a rigid endoscopic instrument such as an endoscopic cutting tool or endoscopic electrode through the dome of the valve and straight down to the attached catheter. Thereafter, the obstruction can be cleared by cutting, cauterizing, or coagulating using the endoscopic instrument.
In addition, it is well known that infection is a well known complication associated with hydrocephalus shunts. It is well known that infections occur in about 5% to about 10% of all hydrocephalus shunt implantations. It is believed that a majority of these infections occur via transmission from microbes upon the surgical gloves, the patient's skin, implants or instruments. Unlike routine systemic infections, infections associated with implants (“periprosthetic infections”) are particularly troublesome.
Therefore, it is an object of the present invention to provide an orthopedic implant and a hydrocephalus shunt adapted to prevent and/or treat occlusions and infections.